6-89
b. A TRIG LEVEL and B TRIG LEVEL from the DAC System (schematic diagram 6) via
A10U640A (A TRIG LEVEL) and A10U640D (B TRIG LEVEL) and filter networks R250-C250 or
R162-C160 is another. These voltage levels should be adjustable from -1.3 V to + 1.3 V using
the FORCE DAC function.
a. ATHO (A Trigger Holdoff) from the Trigger Holdoff circuit (schematic diagram 13) to AlB Trigger
Generator U150 through a level shifting resistor string of R225 and R134. The level at U150
pin 15 is less than +3.3 V for logic LO and greater than +4.0 V for logic HI. The input must be
logic HI for a trigger output to occur. If the ATHO signal is not correct, see the "HOLDOFF
PROBLEMS" in Procedure 4.
Common to both the external trigger signal path and the internal trigger signal path is AlB Trigger
Generator A1OU150(schematic diagram 11) with the following related input signals:
1. For this test to result in a PASS flag, several major circuit blocks must work correctly.
External and Internal Trigger Path (common circuitry):
Troubleshooting Procedure:
NOTE
TRIGGER MODE is set to A and B to program A TG output to
be
the AND of A and B
triggers. Thus ATG may be tested as an indication that triggering has occurred. This
requires that BOTH A AND B TRIGGERS MUST BE FUNCTIONAL TO GET EITHER
TEST RESULT TO PASS.
Triggers have constants for offset and gain. The value of Level DAC output that caused the trigger to
change state is assumed to be the upper hysteresis level in plus slope and the lower hysteresis level in
negative slope.
IF A SELF DIAG OR EXTENDED DIAG TEST FAILS, ONE CANNOT ASSUME THE HARDWARE IS
DEFECTIVE UNLESS THE SAME TEST FAILS A SELF CAL. The reason that SELF CAL must be run
to assure a hardware failure is that SELF CAL computes new values of the constants for each test
and uses them in the subsequent tests. Whereas, diagnostic tests use previously stored constants for
making the tests. If those stored values are not valid for the present operating temperature of the
scope, the test may not be able to converge to a solution.
The Triggers tests, if passed, indicate that the analog trigger circuitry is functional.
Testing Method:
AlB Trigger Generator AlOU150 (schematic diagram 11):
9000
TRIGGERS
8. Shift Registers U221 and U511 are assumed functional with proper input signals if there is a
PASS flag present at the 2520 level of the Extended Diagnostics menu after performing the EXT
DIAG diagnostics test. Otherwise, troubleshoot the Shift Registers for the source of failure.
7. Check the ADEN CLK line for the presence of a signal at the times when an audible click should
be heard.
6. If none or only some audible clicks were heard, and assuming the Attenuator Register and
Preamplifier tests passed the Power-on SELF TEST or a subsequent EXTENDED DIAGNOSTIC
test, troubleshoot the magnetic-latch buffers (U510 and U220) and the latching circuitry (0620,
0621, U520, and associated components) on diagram 9.
Table 6-6 (cont)
Maintenance-2430 Service
To Next Page
Loading...
